Virtual screen display device

ABSTRACT

A virtual screen display apparatus includes a display arranged to generate display information and having an effective diagonal length DLC and an optical projecting element arranged to receive the display information from the display and to project and form an image, the optical projecting element having an effective F number which is defined by Fe=S1/PuD wherein S1 is a distance between the display and a principal point of the optical projecting element and PuD is a diameter of an exit pupil of the optical projecting element. A field optical element arranged to form an in-space image in a position of a virtual screen and to direct a divergent light flux from the virtual screen to a view region where the image is viewable to an observer. A diameter of a range in which the image is viewable to the observer in the view region is ERD and a diagonal length of the virtual screen is VSD and a distance between the virtual screen and the view region is VSP, and the following equation is satisfied: 
     
       
           VSD/VSP=DLC /( ERD×Fe ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 09/138,954filed Aug. 24, 1998 now U.S. Pat. No. 6,292,305.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to a display device which displays anoutput, such as characters or image information, from an output devicesuch as a computer, a television (TV), a video player, an optical discdrive, a TV phone, a TV or computer game and the like, and moreparticularly, the present invention relates to a virtual screen (VS)display device which enlarges and displays an image in space as anobserved image while a background behind the VS display device can besimultaneously observed. The VS display device can be a VS stereoscopicdisplay device and is applicable to a head-up display (HUD), a headmount display (HMD), a projector type color image display device, aliquid crystal projector, a portable display and other display devices.

2. Description of Related Art

Conventional virtual screen display devices are known in which an imagedisplayed on a cathode ray tube (CRT), a liquid crystal display element(LCD) or another image display is enlarged and displayed in space as anobserved image, rather than a displayed image as displayed on the CRT orLCD or the like, by using a hologram combiner or another combiner andsuch that a background located behind or on the rear side of thecombiner can be simultaneously observed or seen while viewing an imagedisplayed on the virtual screen display device. Also, a display devicefor enlarging and projecting a three-dimensional image is known.

For example, a display system described in Japanese Patent ApplicationLaid-open Publication No. 1-147421/1989 uses a volume phase hologram orthe like as a light flux combining element to polarize only a light fluxhaving a specified wavelength and project the specified wavelength lightflux toward an observer. The observer can observe the displayedinformation and another person's face in the same field of view whilethe displayed information can not be viewed or read by the other person.

A display device described in Japanese Patent Application Laid-openPublication No. 8-201722/1996 is provided with an optical filterincluding a plurality of surface-splitting filter portions havingdifferent transmission wavelengths and a hologram combiner whichdisplays virtual images of a plurality of display images which aretransmitted through the filter portions of the optical filter in adifferent position or substantially the same position as that seen by anobserver.

A three-dimensional image projecting device described in Japanese PatentApplication Laid-open Publication No. 9-243961/1997 is provided with aprojecting lens for enlarging and projecting a three-dimensional image,a first concave mirror forming an enlarged virtual image of the imageoutput from the projecting lens and a second concave mirror forming areal image of an image output from the projecting lens. It is furtherdescribed that in the three-dimensional image projecting device, firstand second holograms are used instead of first and second concavemirrors such that the virtual image of the projecting lens is positionedat the center of curvature of the second concave mirror and such thatthe first and second holograms are arranged to be connected to eachother.

In JP 1-147421/1989, since a volume phase diffraction grating is used asthe combiner, a substantially plane surface must serve in the samemanner as a spherical surface. Therefore, a display light flux isdirected toward the observer's eyes even when the combiner is arrangedvertically. However, the display has a disadvantage in that the displaycan be performed only within a specified wavelength.

In JP 8-201722/1996 described above, an optical filter similar to adisplay information color filter is divided into a plurality of regions,but the image divided into regions on the optical filter can bedisplayed at substantially the same position by laminating or exposingmultiple layers of the hologram combiner for each wavelength. Therefore,a full-color display is possible. On the other hand, since the imagedisplayed on an LCD or CRT is displayed as a virtual image as it is, theLCD or CRT must be enlarged while maintaining high resolution whichresults in significantly increased cost. Furthermore, a broad, uniformand highly luminous light source is necessary for such an apparatus forproper viewing of the virtual image. Such a light source is technicallycomplicated and significantly increases the cost of the apparatus.

In JP 9-243961 described above, although the structure is applied to athree-dimensional image projecting device, a field optical element mayinclude a concave mirror or a reflective hologram, i.e., an opticalsystem of a so-called VS (virtual screen) display device. In thisdevice, two components of the concave mirror or the hologram are used toenlarge an observation view region. Specifically, the optical systemincludes the first concave mirror for forming the enlarged virtual imageof the projecting lens and the second concave mirror for forming thereal image of the projecting lens, and the observation view region isenlarged by locating the virtual image of the projecting lens in thecurvature center of the second concave mirror. However, in this device,a projected object is enlarged about 1.94 times while the observationview field is enlarged twice or about 2.0 times. Therefore, adistinguishing effect cannot be obtained and the image is not easilyviewable. Strangely, the magnitude of the projecting lens is notexpressly described in this reference, although the projecting lensactually has a size of an exit pupil. Therefore, it is uncertain howmuch or to what degree the observation view region is enlarged ascompared with the related devices described above. Even assuming that anF number of the projecting lens is set to F=1.4, a focal distance f is300 mm, then the observation view region is 429 mm when the diameter ofthe exit pupil is 214 mm. Although this is a good value, such level canbe realized without using two concave mirrors as described later in thepreferred embodiments of the present invention. Moreover, the use of twoconcave mirrors and locating the virtual image of the optical projectingelement formed by the first concave mirror in the curvature center ofthe second concave mirror excessively restricts the freedom in designingan optical system layout. This means that the possibility of developingvarious applications is remarkably reduced.

In another related device, conventional projection type color imagedisplay devices using a liquid crystal panel are known to use either athree-plate system or a single-plate system. In the three-plate system,three liquid crystal panels are used, and three color component images,i.e., red, green and blue images of a color image to be displayed aredisplayed on the individual liquid crystal panels. These three liquidcrystal panels are separately irradiated with red, green and bluelights, and the red, green and blue lights transmitted through theliquid crystal panels are focused by a common image forming lens tosynthetically form an image on a screen, and thereby a color image isdisplayed.

In the single-plate system, one liquid crystal panel (single-plateliquid crystal panel) is used. Red, green and blue component images aresimultaneously displayed on the single-plate liquid crystal panel. Thered component image is irradiated with a red light, the green componentimage is irradiated with a green light and the blue component image isirradiated with a blue light. The red, green and blue light forirradiation is obtained from a single white light source and by using acolor separator as described below. Light fluxes transmitted through thesingle-plate liquid crystal panel are focused by a common image forminglens to form an image on a screen, and thereby a color image isdisplayed.

In the three-plate system, since the red, green and blue componentimages are separately displayed on the three liquid crystal panels, eachcomponent image can be displayed with a high picture element density.The quality color image having a high picture element density can bedisplayed, but the cost is significantly increased because the threeliquid crystal panels are used.

The single-plate system can be provided for a relatively low cost.However, since the three color component images are simultaneouslydisplayed on one liquid crystal panel, it is difficult to increase thepicture element density of the displayed color image.

Furthermore, in both the single-plate system and the three-plate system,a white light from a white light source is color-separated into red,green and blue lights. Since a space for the color separation and anamount of heat generated at the white light source are large, a coolingdevice for cooling the white light source exclusively and a largecooling space are necessary, which greatly enlarges the color imagedisplay device.

Moreover, in the single-plate system, color-separated light fluxes aremade incident at mutually different angles on the single-plate liquidcrystal panel. Therefore, the color separation of the white light isvery difficult.

In addition, as described above, display devices for displaying astereoscopic image are known. Various three-dimensional display systemsare disclosed in the article titled “Three-dimensional Display—VariousSystems and Application to Television,” Journal of the TelevisionSociety Vol.41, No. 7, p. 610-618 (1987). This article includes apicture of a stereoscopic vision system without glasses using a concavemirror in FIG. 2(i) on page 611. It is further described on page 612that there is a system in which screen images of two projectors areformed in an interval between both eyes, respectively, by using a largeconcave mirror or a large convex lens of FIG. 2(i).

In a stereoscopic image display device described in Japanese PatentApplication Laid-open Publication No. 8-5956/1996, space modulationelements (display elements) for right and left eyes are disposedsubstantially at a right angle relative to each other, and between whicha half mirror combiner is disposed. A light emitting device as a backlight is placed on the side of a rear surface of each space modulationelement and each light emitting device is provided with a light emittingregion for one eye and a non-light emitting region for the other eye. Anoptical element with a directivity for enlarging the light emittingregion is disposed between the space modulation element and the lightemitting device, and images presented for right and left eyes aredirected toward the right and left eyes, respectively, in such a mannerthat a stereoscopic image can be seen without using polarizing glassesor the like. It is also described that the back light is lit in atime-sharing manner and that an optical control device is provided withthe light emitting region for one eye and the non-light emitting regionfor the other eye is disposed between each light emitting device and thespace modulation element and that the optical element having thedirectivity for guiding the light from each transmission region towardeach eye is applied before a half mirror. A transmission region of theoptical control device is time-shared and a polarizing device isprovided on a front surface of a display surface of each display elementto introduce orthogonal straight polarized lights into the half mirrorand the optical control device having a region which is divided intoright and left regions for passing only each polarized light is placedon the front surface of the half mirror.

A single-eye observation view distance-adjusting display devicedescribed in Japanese Patent Application Laid-open Publication No.8-146348/1996 is provided with at least an original image forming unit,a projection lens and an optical pupil mapping device. The optical pupilmapping device is arranged in such a manner that a pupil of theprojection lens is mapped to at least one eye pupil of an observer andthat a single-eye observation view distance is adjusted independently ofa position of the optical pupil mapping device by adjusting an imageforming position of the projection lens for an original image. A naturalstereoscopic view can be realized by matching the single-eye observationview distance to a both-eye observation view distance and a clearstereoscopic image can be obtained without using special glasses or alenticular lens.

In Japanese Patent Application Laid-open Publication No. 8-186849/1996,a transmission type stereoscopic visual device without using polarizingglasses is disclosed. Polarizing members each having a polarizingdirection which is perpendicular to an adjoining polarizing directionare arranged in a stripe configuration on the side of a rear surface ofa screen and lenticular lens plates having a pitch equal to a width ofthe stripe are disposed on the side of a front surface of the screen. Aleft-eye projection light for a left eye and a right-eye projectionlight for a right eye each having a polarized light aligned in thepolarizing direction are projected on the screen via a projector.

In JP 8-5956 described above, the space modulation elements (displayelements) for both eyes are arranged at a substantially right anglebetween which the half mirror combiner is disposed. The light emittingdevice for the back light is placed on the side of the rear surface ofeach space modulation element. Although it is not clear why, each lightemitting device is provided with the light emitting region for one eyeand the non-light emitting region for the other eye. The optical elementwith the directivity for enlarging the light emitting region is disposedbetween the space modulation element and the light emitting device.Images presented for right and left eyes are directed to the right andleft eyes, respectively. Therefore, a stereoscopic image can be seenwithout using the polarizing glasses or the like, but the luminousenergy is reduced by half or more because the half mirror is used.Furthermore, a control of the light emitting region and the non-lightemitting region in order not to overlap right and left images and othervarious features are described. However, this has little effect althoughthey have a relatively large-scale constitution.

JP 8-146348 describes, by referring to the Journal of Television Societyarticle described above, that it is known that the screen images of twoprojectors are formed in the interval between both eyes by using aconcave mirror or a positive lens. Then, it is described that the deviceis constituted in such a manner that when the position in which theimage of an original image is formed by the projection lens is adjusted,the single-eye observation view distance is adjusted independently ofthe position of the optical pupil mapping device. It is furtherdescribed that by matching the single-eye observation view distance withthe both-eye observation view distance, a natural stereoscopic view isrealized and a clear stereoscopic image can be obtained without usingspecial glasses or the lenticular lens. However, although the matchingof the single-eye observation view distance with the both-eyeobservation view distance and its method are detailed, it is notdescribed in detail how two view regions are arranged.

In JP 8-186849, the polarizing members each having the polarizingdirection which is perpendicular to the adjoining polarizing directionare arranged in the stripe configuration on the side of the rear surfaceof the screen while the lenticular lens plates having the pitch equal tothe width of the stripe are disposed on the side of the front surface ofthe screen. The left-eye projection light for the left eye and theright-eye projection light for the right eye each having a polarizedlight aligned in the polarizing direction are projected on the screenwith the projector. Therefore, the transmission type stereoscopic visualdevice without using the polarizing glasses is realized. However, sincethe polarized light is used and the screen is divided into two sections,the luminous energy is reduced to a quarter or even more. Furthermore,since the device is of the rear-surface projection type, the totalsystem is disadvantageously enlarged (lengthened).

SUMMARY OF THE INVENTION

In order to overcome the problems described above, the preferredembodiments of the present invention provide a virtual screen displaydevice which projects and forms an image of an object image displayed ona relatively small image display for displaying characters or imageinformation in a predetermined space so that a real in-space image isobserved in a desired position by an observer and so that the observedimage is bright, attractive, easy on the observer's eyes to view forlong periods of time, high in confidentiality and consumes relativelylittle energy by defining a relationship between components of such adevice to construct a virtual screen (VS) display system effectively andto achieve the above-identified advantages.

According to a preferred embodiment of the present invention, a virtualscreen display apparatus includes a display arranged to generate displayinformation and having an effective diagonal length DLC, an opticalprojecting element arranged to receive the display information from thedisplay and to project and form an image, the optical projecting elementhaving an effective F number which is defined by Fe=S1/PuD wherein S1 isa distance between the display and a principal point of the opticalprojecting element and PuD is a diameter of an exit pupil of the opticalprojecting element and a field optical element arranged to form anin-space image in a position of a virtual screen and to direct adivergent light flux from the virtual screen to a view region where theimage is viewable to an observer, wherein a diameter of a range in whichthe image is viewable to the observer in the view region is ERD and adiagonal length of the virtual screen is VSD and a distance between thevirtual screen and the view region is VSP, and the following equation issatisfied:

VSD/VSP=DLC/(ERD×Fe).

In a further preferred embodiment, the following relationship issatisfied:

0.08<DLC/(ERD×Fe)<0.6.

Moreover, in the virtual screen display device of the invention, theimage display is preferably a cathode ray tube (CRT), a liquid crystaldisplay element (LCD), a digital mirror device (DMD) or anotherrelatively small display which can display an output from an outputdevice such as a computer screen or a television, the output includingcharacters and image information.

The optical projecting element is preferably constructed to enlarge andproject the image of an object displayed by the display devicesmentioned above and preferably comprises one of a projecting lens, apositive lens, a reflective image forming element, a Fresnel opticalsystem, a hologram, and a concave mirror. Furthermore, the opticalprojecting element preferably comprises a single lens but may comprisemore than one lens.

Similarly, the field optical element preferably comprises a single lensbut may comprise more than one lens. Furthermore, the field opticalelement is preferably arranged such that an image of the in-space imageis created at a retina of the observer when the retina of the observeris positioned in the view region.

According to another preferred embodiment of the present invention, aprojector type color image display device is constructed and arranged tohave an extremely compact configuration while displaying a high qualitycolor image with a high picture element density by using a single spacemodulation element and eliminates the need for difficult colorseparation. This preferred embodiment provides a projector color imagedisplay device including a space modulation element having a twodimensional arrangement of picture elements which are adapted to displayan image to be displayed as a two-dimensional transmittancedistribution, a red light source (R light source) which outputs a redlight, a green light source (G light source) which outputs a green lightand a blue light source (B light source) which outputs a blue light, adichroic prism arranged to selectively reflect or transmit therespective lights from each of the respective R light source, G lightsource and B light source, an image forming lens arranged to projectlight fluxes transmitted through the space modulation element to form animage, an image information input element constructed to input imageinformation of the image to be displayed to the space modulationelement, a light source drive arranged to turn on and off the R lightsource, the G light source and the B light source and a controllerarranged to control the image information input element such that a redcomponent image, a green component image and a blue component image of acolor image to be displayed are successively or selectively switched anddisplayed on the space modulation element and arranged to control thelight source drive to successively or selectively switch on and off theR light source, the G light source and the B light source andperiodically repeat the lighting in such a manner that only the R lightsource is lit when the red component image is displayed on the spacemodulation element, only the G light source is light when the greencomponent image is displayed and only the B light source is lit when theblue component image is displayed.

The R light source, the G light source and the B light source preferablyinclude LEDs which are adapted to emit red light, green light and bluelight, respectively.

Since the three light sources which separately radiate the red, greenand blue lights are used, color separation, which is required in theprior art using a white light source emitting a white light, is notrequired to be performed.

The R light source, the G light source and the B light source and thespace modulation element are arranged to surround the dichroic prism.

The dichroic prism is preferably a substantially rectangularparallelpiped prism element which is arranged to selectively reflect ortransmit the red light from the R light source, the green light from theG light source and the blue light from the B light source to irradiatethe space modulation element. Specifically, the red, green and bluelights from the R, G and B light sources are synthesized by the dichroicprism to irradiate the space modulation element. The substantiallyrectangular parallelepiped prism preferably includes a dichroic filterfilm for at least two of red, green and blue light sources, wherein eachof the dichroic filter films is adapted to reflect a selected one of thered, green and blue lights and transmit the others of these lights.

The image information input is a device used to input the information ofthe image to be displayed into the space modulation element. The imageinformation may include images, data, information, etc. which has beencreated by a computer, a word processor or the like, and whichinformation is capable of being read as image information from a floppydisc, an optical disc or other suitable storage medium or read via animage scanner or the like.

The controller may comprise a computer, an exclusive CPU, amicroprocessor or other suitable control device.

Moreover, the light source drive is preferably constructed and arrangedto change a light emitting intensity of each light source (R lightsource, G light source and B light source). In this case, the lightemitting intensity can be manually adjusted. Furthermore, a light sourcesuch as a cold cathode tube, a fluorescent tube or electroluminescencecan also be used.

Moreover, although various known space modulation elements can be used,a liquid crystal panel is especially preferred. In this case, a microlens array for enhancing an incident efficiency of an irradiation lightof each picture element can be provided on an incident side of anirradiation light of the liquid crystal panel. Furthermore, the R, G andB light sources can have cooling devices such as a negative coolingdevice like a cooling fin for radiating a heat from a base whichsupports the LEDs or a positive cooling device such as a Peltier elementand a cooling fan or a provision of both the positive cooling device andthe negative cooling device. When both the negative and positive coolingdevices are provided, the positive cooling device may be used only in acontributory manner as required.

The projector type color image display device of preferred embodimentsof the present invention may include a display medium to which an imageforming light flux is projected from the image forming lens. A screen, aconcave mirror or a hologram combiner (a flat panel of a hologram forcorrecting the deflection of the displayed color image and synthesizingan image behind the panel and the displayed color image for observation)may be used as the display medium. The display medium preferably has adiagonal length of about 30 inches or less. A half mirror or alenticular screen (screen having small-diameter beads embedded in ascreen plane and having a high directivity of a reflected light) is alsopreferably used.

In the projector type color image display device of preferredembodiments of the present invention, the space modulation element, theR, G and B light sources, the dichroic prism and the image forming lenscan be disposed on the same base. In this case, the image informationinput, the light source drive, the controller and an electric systemlike a power source may be separated from a projector body section.

According to another preferred embodiment of the present invention, avirtual screen stereoscopic display device is arranged and constructedto be compact, low in cost and energy-saving and to easily produce aclear stereoscopic image without using special glasses or a lenticularlens. More specifically, such a preferred embodiment of a virtual screenstereoscopic display device includes at least two displays arranged todisplay characters and image information, at least two opticalprojection elements arranged to enlarge, project and form real images ofobject images displayed by the at least two displays in a display space,the real images formed by the at least two optical projection elementsbeing projected in-space images, and at least one optical focusingsystem arranged to position light fluxes received from the two projectedin-space images at two predetermined view regions, respectively, whereincenters of the two view regions are spaced apart from each other in atransverse direction and the two view regions overlap each other in thetransverse direction.

In a specific example of a preferred embodiment of the presentinvention, the virtual screen stereoscopic display apparatus is arrangedsuch that the centers of the two view regions are spaced from each otherby an approximate distance of about 60 mm to 70 mm and are overlapped byabout 7 mm or less.

It is preferable that each of the two displays of the virtual screenstereoscopic display apparatus includes at least one of a cathode raytube, a liquid crystal display, a digital mirror device and a displaymeans which can display an output from a computer, a television ordisplay generating device. Each of the displays is adapted to displayimages independently and can display the same or different images asrequired. The two displays are preferably arranged to display right-eyeimage information on a left side and left-eye image information on aright side when a person is opposed to the two displays.

The optical focusing system includes at least one of a concave mirror, areflective image forming element, a positive lens, a transmission typeimage forming element, a Fresnel optical element, a hologram and anoptical diffraction element.

For the purpose of illustrating preferred embodiments of the presentinvention, there is shown in the drawings several forms which arepresently preferred, it being understood, however, that the invention isnot limited to the precise arrangements and instrumentalities shown.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view illustrating an optical arrangement of avirtual screen display device according to preferred embodiments of thepresent invention.

FIG. 2 is an explanatory view showing a basic concept of a virtualscreen display device related to preferred embodiments of the presentinvention.

FIGS. 3A and 3B are explanatory views showing an example of anapplication of the virtual screen display device of preferredembodiments of the present invention.

FIG. 4 is an explanatory view showing another example of an apparatusincluding the virtual screen display device of preferred embodiments ofthe present invention.

FIG. 5 is an explanatory view showing a further example of an apparatusincluding the virtual screen display device of preferred embodiments ofthe present invention.

FIG. 6 is an explanatory view showing still a further example of anapplication of the virtual screen display device of preferredembodiments of the present invention.

FIG. 7 is an explanatory view showing still a further example of apractical application of the virtual screen display device of preferredembodiments of the present invention.

FIG. 8 is an explanatory view showing still a further example of anapparatus including the virtual screen display device of preferredembodiments of the present invention.

FIG. 9 is an explanatory view showing still a further example of anapparatus including a virtual screen display device of preferredembodiments of the present invention.

FIG. 10 is an explanatory view showing still a further example of anapparatus including a virtual screen display device of preferredembodiments of the present invention.

FIG. 11 is an explanatory view showing still a further example of anapplication of the virtual screen display device of preferredembodiments of the present invention.

FIGS. 12A and 12B are explanatory views showing still further examplesof applications of the virtual screen display device of preferredembodiments of the present invention.

FIG. 13 is an explanatory view showing still a further example of anapparatus including the virtual screen display device of preferredembodiments of the present invention.

FIG. 14 is an explanatory view showing still a further example of anapparatus including the virtual screen display device of preferredembodiments of the present invention.

FIG. 15 is a schematic drawing of a projection color image displaydevice according to a preferred embodiment of the present invention.

FIG. 16 is a isometric plan view of the structural configuration of thepreferred embodiment shown in FIG. 15.

FIG. 17 is an explanatory view of an arrangement of a virtual screenstereoscopic display device according to a preferred embodiment of thepresent invention.

FIG. 18 is a view showing a basic concept of the virtual screen displaydevice according to preferred embodiments of the present invention.

FIG. 19 is an explanatory view of an arrangement of a virtual screenstereoscopic display device according to another preferred embodiment ofthe present invention.

FIG. 20 is an explanatory view of an arrangement of a virtual screenstereoscopic display device according to still another preferredembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail with reference to the accompanying drawings.

FIG. 2 is a diagram showing a basic concept of a virtual screen (VS)display device related to preferred embodiments of the presentinvention. FIG. 2 illustrates an example of a VS display optical systemwhich is provided with an image display 1 for displaying imageinformation, an optical projecting element 2 for projecting and formingan image of an object image displayed on the image display 1 in a viewregion and a field optical element 3 for directing a light flux from thein-space image projected by the optical projecting element 2 toward anobserver's eyes.

The image display 1 may comprise a cathode ray tube (CRT), a liquidcrystal display element (LCD), a digital mirror device (DMD) or otherdisplay devices which are adapted to display an output includingcharacters and image information which are output from an apparatus suchas a computer or a television (TV). When the image display 1 is a CRTwhich itself emits light, an additional lighting source or system is notnecessary. However, when the image display 1 is an LCD as shown in FIG.2, a lighting system 1B including a lighting source, a diffusion plate,a filter and other elements is located at the rear surface of thedisplay 1A comprising an LCD. When the image display 1 is a DMD, aspecial optical system for radiating light to the DMD obliquely from afront surface is necessary.

Furthermore, the optical projecting system 2 enlarges and projects animage output from the CRT or other display which itself emits light oran LCD, DMD or another display apparatus which outputs an image which istransmitted or reflectively lightened by the light source or systemdescribed above.

The field optical element 3 is arranged to direct the light flux, whichis to be formed as an image at a real screen position 4 (the position atwhich an image is formed when no field optical element is present),located at the observer's eyes. The field optical element 3 is arrangedto change the direction of the light flux with a positive power, form anin-space image in a position of a virtual screen (VS) 5 (the image ofthe real screen as an object via the field optical element 3), and bringa divergent light flux from the virtual screen into a view region 6within a range in which the observer's eyes are to be placed. In theexample of FIG. 2, a positive lens or another transmissive image formingelement is shown as the field optical element 3, but a concave mirror oranother reflective image forming element, a Fresnel optical system, orhologram or another diffraction optical element or similar device canalso be used as the field optical element.

Examples of applications or apparatuses in which the virtual screen (VS)display device of preferred embodiments of the present invention isincorporated to construct various types of display devices will bedescribed below.

FIGS. 3A and 3B show an example in which the VS display device accordingto preferred embodiments of the present invention is applied to aportable television (TV). FIG. 3A shows an example of a portable TV 7using a positive lens as a transmissive image forming element for thefield optical element 3 in which a display image of the image display 1comprising an LCD or other display can be seen as an in-space image inthe position of the virtual screen 5.

FIG. 3B shows an example of a portable TV 9 using a reflective imageforming element (e.g., a concave mirror) as the field optical element 8,in which a TV body is arranged to have a projector configuration of theimage display 1 and the optical projecting system 2 and an imageprojected by the projector configuration can be seen as an in-spaceimage in the position of the virtual screen 5 via the field opticalelement 8 which includes a reflective image forming element installedoutside of the TV body.

In the preferred embodiment shown in FIG. 3A, since the optical systemis contained completely within the TV body, miniaturization can beattained, but a position in which an observer M can view the image isrestricted. The preferred embodiment of FIG. 3B is slightly bulkybecause the reflective field optical element 8 is mounted outside of theTV body, but the degree of freedom in adjusting the position at whichthe observer M views the image is significantly increased by adjustingthe position or angle of the field optical element 8.

FIG. 4 shows an example in which the VS display device is applied to aportable TV phone, in which a projector section 11 including an imagedisplay, an optical projecting element and the like is provided in a TVphone body and a reflective field optical element (e.g., a concavemirror) 12 is mounted outside of the body. In this example, when thereflective field optical element 12 is formed of polycarbonate oranother resin material, the TV phone has a very light weight, isextremely portable and can be operated with one hand. Additionally, inthe portable TV phone for transmitting an image in addition to receivingan image, a photographing camera such as a CCD or another micro-camerais preferably mounted on the rear surface of the reflective fieldoptical system 12 or the like. Furthermore, in FIG. 4 a phone sectionand a display device are integrally shown, but a general cellular phonecan be mounted on the display device to comprise the phone section.

FIG. 5 shows an example of preferred embodiments of the presentinvention in which the VS display device is a display device for a smallmobile computer. In this example, a projector section 14 including animage display, an optical projecting element and the like is provided ina body of a display device 13 and a reflective field optical element(e.g., concave mirror) 15 is mounted outside of the body. A mobilecomputer 16 is preferably separate from the display device 13 and themobile computer 16 can be removed from the display device 13 forindependent use. Furthermore, when a modem is built in the displaydevice 13, image information can be received and displayed by the mobilecomputer 16 by connecting a cellular phone 17 thereto. Moreover, byconnecting a CCD or another micro-camera to the device shown in FIG. 5,the device can transmit a photographed image or can operate as a TVphone.

FIG. 6 shows an example of preferred embodiments of the presentinvention in which the VS display device is provided with a portablevideo player (video tape player, digital video disc (DVD) player) orsimilar apparatus. A projector section 19 comprising an image display,an optical projecting element and the like is provided in a body of avideo player 18, and a reflective field optical element (e.g., a concavemirror) 20 is preferably attached outside of the body.

FIG. 7 shows an example of preferred embodiments of the presentinvention in which the VS display device comprises a display device of alaptop or notebook personal computer. A projector section 22 includingan image display, an optical projecting element and the like is providedin a body of a computer 21, and a reflective field optical element(e.g., a concave mirror) 23 also serving as a lid for the laptop ornotebook computer is preferably attached outside of the computer body.The weight of the computer device can be reduced and an amount of energyused can be saved with this configuration as compared with a directvision display using a typical LCD provided with a back light.

FIG. 8 shows an example of preferred embodiments of the presentinvention in which the VS display device comprises a display device of adesktop personal computer or similar apparatus. A projector section 25including an image display, an optical projecting element and the likeis provided in a desk 24, and a reflective field optical element (e.g.,a concave mirror, a reflective hologram or the like) 26 is attached onthe desk. In this case, the device occupies less space on the desk ascompared to a conventional display such as a CRT or another conventionallarge-sized display is used. By adjusting the reflectance of thereflective field optical element 26, the background can be seen.

FIG. 9 shows an example of preferred embodiments of the presentinvention in which the VS display device comprises a display deviceprovided on a seat of a taxi, car or other vehicle. A projector section28 including an image display, an optical projecting system and the likeis preferably provided to be viewed by an observer sitting in the backseat, and a reflective field optical element (e.g., a concave mirror) 29also serving as a protective glass is preferably installed between adriver's seat and the back seat. In this case, by adjusting thereflectance of the reflective field optical element 29 serving also asthe protective glass, conditions in front of the car and an displayedimage can be simultaneously seen.

FIG. 10 shows an example of preferred embodiments of the presentinvention in which the VS display device comprises a display device fora seat of an aircraft or other seat viewing configuration. A projectorsection 31 including an image display, an optical projecting element andthe like is provided in an arm or other part of a seat 30, and areflective field optical element (e.g., a concave mirror) 32 ispreferably attached to the ceiling. In this case, the reflective fieldoptical element 32 is moved together with a backrest of the seat 30 by adrive device 33. When the backrest is set upright, the field opticalelement moves toward the ceiling and does not become an obstruction, andwhen the backrest is inclined, the field optical element moves toward adisplay position. When a CRT, an LCD or another conventional displaydevice is used in the dark in the aircraft during a night flight or whenthe aircraft cabin is not well-lit, light leaks from an image plane tobother others. In the VS display device of preferred embodiments of thepresent invention as shown in FIG. 10, however, the view region is sonarrow that only the observer M can see the image, and the device doesnot bother others on the aircraft.

FIG. 11 shows an example of preferred embodiments of the presentinvention in which an image plane of a desktop VS display device similarto the device shown in FIG. 8 is enlarged, and the VS display device isinstalled in a capsule office or the like. In the VS display device, thesize of an image plane of an image display element in a projectorsection 36 is enlarged, and a large-sized reflective field opticalelement 37 is installed. The enlargement of the image plane is thuspossible. Since the occupying space on a desk 35 is significantlyreduced as compared with a conventional CRT having a large image plane,in the capsule office or the like having no window, by installing thelarge-sized reflective field optical element 37 on a wall surface anddisplaying a landscape or another image, a user can work without feelingoppressed or claustrophobic even in the narrow capsule office. Moreover,if a notebook computer or the like is connected to the projectorsection, an image being output by the computer can be displayed on theVS display device.

FIGS. 12A and 12B show an example of preferred embodiments of thepresent invention in which the VS display device comprises a displaydevice in a relaxation capsule. A projector section 40 including animage display, an optical projecting element and the like is providedpreferably beside a pillow in a capsule 38, and a concave surface of aspherical window of the capsule 38 is used as a reflective field opticalelement 39. In this case, since a person M can see an image displayed ona virtual screen 5 and the outside of the window simultaneously, he canrelax without feeling oppressed or claustrophobic even in a narrowcapsule space.

FIG. 13 shows an example of preferred embodiments of the presentinvention in which the VS display device is installed on a bed in ahospital or the like. A projector section 41 including an image display,an optical projecting element and the like is provided beside a pillowor the like of the bed, and a reflective field optical element (e.g., aconcave mirror) 42 is movably supported on a stand 43. In this example,since the position of the reflective field optical element 42 can beoptionally adjusted and set, a virtual screen 5 can be set in a positionwhere a patient can most easily see the screen while lying in the bed.When the conventional CRT or LCD is used in a common room or the like inthe hospital, a light leaks from an image plane and bothers otherpatients, but in the VS display device of preferred embodiments of thepresent invention, a view region is so narrow that only an observerlying in the bed upon which the display is mounted can see an imagedisplayed thereby, and the device does not bother others.

FIG. 14 shows an example of preferred embodiments of the presentinvention in which the VS display device comprises an executive displayinstalled in a President's room, a Director's room or the like. Aprojector section 44 includes an image display, an optical projectingelement and the like and is provided on or in a desk 46, while alarge-sized reflective field optical element (e.g., a concave mirror) 45is installed on the desk. Since the projector section 44 is connected toa video camera which is installed in an neighboring secretary's room, asecretary's face is displayed on an in-space virtual screen to informthe President or Director that a visitor is coming and the visitor'sface can also be displayed if necessary so that the President orDirector can see the visitor. Additionally, a person can usually workwhile facing an image plane of a personal computer or the like displayedon the screen, or an image plane of TV or video can also be displayed.Moreover, when the reflectance of the reflective field optical system 45is set to be relatively low, the background can be seen, and when theimage display is unnecessary, the outside of the window or the likebehind the reflective field optical system 45 can be seen.

Various application examples of the VS display device according topreferred embodiments of the invention have been described. The VSdisplay device can be used in many different types of devices covering abroad spectrum of products from a portable type display with a smallimage-plane size to an installation type display with a largeimage-plane size. Therefore, it is important to design the opticalsystem in accordance with a particular use or application, and it isnecessary to clarify a physical range in which the principle of the VSdisplay system effectively works. However, as will be described below,it has been extremely difficult to design, arrange and construct such aVS display device for any particular use or application.

In the virtual screen (VS) display device using the basic principleshown in FIG. 2 including the display 1, the optical projecting element2 and the field optical element 3, in such prior art devices, it wasnecessary to conduct trial and error processes in order to plan anddesign the characteristics and arrangement of each of the elements 1-3in the device in order to obtain a device which functions properly andis capable of forming a clear image at an observer's viewing position.Thus, if the application of the display device shown in FIG. 2 waschanged, it was necessary to change the size, arrangement andconfiguration of the elements shown in FIG. 2 in order to obtain anacceptable display device and to achieve a desired clear image at adesired viewing region. This required a great amount of time and expenseand was very difficult.

To overcome these difficulties, the applicant of the preferredembodiments of the present invention discovered a relationship which,when used, allows for precise definition and determination of thephysical and optical characteristics and configuration and arrangementof the elements of the display device so that no trial and error wasnecessary but an exact arrangement could easily be known through use ofthe unique relationship discovered.

More specifically, it was discovered that an inverse relationship existsbetween a position of the virtual screen 5 and the position of the viewregion 6. This relationship was not known or discovered before. It wasalso discovered that this inverse relationship exists in both thevertical (up and down) direction of FIG. 1 and in a plane perpendicularto the plane of FIG. 1.

Furthermore, the applicant discovered that in addition to the inverserelationship described above, the size and physical characteristics ofthe display 1, the optical projecting element 2 and the field opticalelement 3 are related and that just knowing a diagonal length of thevirtual screen 5 and a distance from the virtual screen 5 to the viewregion 6, an exact relationship between the elements of the displaydevice can be determined using the discovered relationship so that thedevice can be arranged exactly according to the relationship and notrial and error is necessary to arrange and construct the device. Thus,if a certain apparatus or application using such a display device isrequested and the size of the virtual screen 5 and a distance betweenthe virtual screen 5 and the view region 6 is known, the relationshipaccording to preferred embodiments of the present invention can be usedto manufacture the device exactly and without having to resort to trialand error for arranging the various components of the device. Inaddition, it is possible to use the discovered relationship to changethe length of the virtual screen VSD or a diameter of the range in whichthe image is viewable to the observer without having to change thecharacteristics of the display 1, the optical projecting element 2 orthe field optical element 3 which was not possible previously.

The relationship according to preferred embodiments of the presentinvention described above will be described in more detail. As shown inFIG. 1, when an effective diagonal length of the image display 1 is DLC,a diameter of a range or view region 6 in which the image is visible tothe observer (view region diameter) is ERD, a diagonal length of thevirtual screen is VSD, an effective Fe number of the optical projectingelement 2 is Fe=Sl/PuD, in which Sl is a distance of the displayrelative to a principal point of the optical projecting element and PuDis a diameter of an exit pupil of the optical projecting element, and adistance from a virtual screen 5 to a view region 6 is VSP, then thefollowing formula is satisfied:

VSD/VSP=DLC/(ERD×Fe)

By using the above-defined relationship, a view region necessary forvarious applications is secured, while a necessary visual angle issatisfied, while allowing the arrangement and characteristics of theelements of the display device shown in FIG. 1 to be determined exactlyfrom the relationship.

In a further preferred embodiment, the above-identified relationship ismodified to be as follows:

0.08<DLC/(ERD×Fe)<0.6

In the above, the positive lens or another transmissive image formingelement has been described as the field optical element 3, but theconcave mirror or another reflective image forming element can be usedas the field optical element. When the concave mirror (spherical concavemirror) is used as the field optical element of FIG. 1, the curvatureradius R of the spherical concave mirror has the following relationshipwith the focal distance fm of the lens:

R=2fm

Now, preferred embodiments of the VS display device satisfying theaforementioned conditions will be described.

In a first preferred embodiment, a presently available minimum LCD,i.e., a 0.55 type LCD (DLC=0.55 inch, about 14 mm) is used as a displayelement constituting the image display 1. Because of itscompactness/lightness, the first preferred embodiment is used mainly asa display device of the portable TV shown in FIG. 3, the portable TVphone shown in FIG. 4, the small-sized mobile computer shown in FIG. 5or the like.

A projecting lens with a focal distance f1 of about 40 mm and an Fnumber of about 1.2 is preferably used as the optical projecting element2, and an LCD comprising the image display element is placed in Sl=−36mm before the principal point of the lens. Additionally, the focaldistance of the field optical system 3 is preferably set to fm=166.7 mm,and the concave mirror (spherical concave mirror) having a curvatureradius R of about 333 mm is used as the field optical element.

As described above, the LCD is located such that Sl=−36 mm before theprincipal point of the projecting lens while the concave mirrorcomprising the field optical element is placed 250 mm (Sm=−250 mm)behind the principal point, and a view region where the observer's eyesare located is Sm′=500 mm from the concave mirror. Then, the virtualscreen (VS) 5 having a diagonal length VSD of 52.6 mm, i.e., about 2.1inches is floated in space with the VSP of about 270 mm before theobserver's eyes.

In this case, VSD/VSP is 0.194, ERD is 66.7 mm, a (half) angle OAextended by the LCD relative to the projecting lens is 11 degrees andthe effective F number Fe is 1.1. Although it is difficult to correctspherical aberration or comatic aberration, this device according to thefirst preferred embodiment has a significantly improved and sufficientcorrection of spherical aberration and comatic aberration.

Furthermore, the diameter of the view region ERD is 66.7 mm, and may notbe considered to be sufficient relative to a usual distance of about 62to about 65 mm between a person's eyes. However, in the first preferredembodiment, since the image display device is portable, the observer caneasily bring the view region toward his eyes. Therefore, the device hasno special problem.

In a second preferred embodiment, in the same manner as in the firstpreferred embodiment, a 0.55 type LCD (DLC=0.55 inch, about 14 mm) isused as a display element constituting the image display 1. Because ofits compactness/lightness, the second preferred embodiment is usedmainly as the display device of the portable TV shown in FIG. 3, theportable TV phone shown in FIG. 4, the small-sized mobile computer shownin FIG. 5 or other similar devices.

A projecting lens with the focal distance f1 of 40 mm and the F numberof 1.8 is used as the optical projecting element 2, and an LCD is usedas the image display element which is placed at Sl=−32 mm before theprincipal point of the lens. Additionally, the focal distance of thefield optical system 3 is set to fm=190.5 mm, and the concave mirror(spherical concave mirror) having a curvature radius R of 381 mm is usedas the field optical element 3.

As described above, the LCD is located at Sl=−32 mm before the principalpoint of the projecting lens while the concave mirror functioning as thefield optical element 3 is placed 250 mm (Sm=−250 mm) behind theprincipal point, and the view region is Sm′=800 mm from the concavemirror. Then, the virtual screen (VS) 5 having a diagonal length VSD of60.7 mm, i.e., about 2.4 inches is floated in space with the VSP beingabout 444 mm before the observer's eyes.

In this case, VSD/VSP is 0.137, ERD is 71.7 mm, a (half) angle OAextended by the LCD relative to the projecting lens is 12.3 degrees andthe effective F number Fe is 1.4. Furthermore, the diameter of the viewregion ERD is 71.7 mm. Therefore, a slightly broader view region can beobtained as compared with the first preferred embodiment.

In the third preferred embodiment, in the same manner as in the firstand second preferred embodiments, a 0.55 type LCD (DLC=0.55 inch, about14 mm) is used as a display element constituting the image display 1.Because of its compactness/lightness, the preferred embodiment is usedas a display device of a portable TV, a portable TV phone, a small-sizedmobile computer or other suitable device. The third preferred embodimentis the same as the first and second preferred embodiments in the opticalsystem arrangement and the like. Therefore, detailed numerical values ofportions are shown in Tables 1 and 2 below, which lists preferredembodiments, and further description is omitted.

In a fourth preferred embodiment, a 1.35 type LCD (DLC=1.35 inch, about34.3 mm) is used as a display element constituting the image display 1.Because of its high density and moderate compactness/lightness, thefourth preferred embodiment is used mainly as the display device of themobile computer shown in FIG. 5 or a notebook type personal computer,the display device of the portable video player shown in FIG. 6 or thedisplay device installed on the rear seat of a vehicle (passenger's seatin the taxi) shown in FIG. 9.

A projecting lens with the focal distance f1 of 40 mm and the F numberof 1.4 is used as the optical projecting element 2, and an LCD being theimage display element is placed at Sl=−48 mm before the principal pointof the lens. Additionally, the focal distance of the field opticalelement 3 is set to fm=176.5 mm, and the concave mirror (sphericalconcave mirror) having a curvature radius R of 353 mm is used as thefield optical element 3.

As described above, the LCD is placed at Sl=−48 mm before the principalpoint of the projecting lens while the concave mirror functioning as thefield optical element 3 is placed 250 mm (Sm=−250 mm) behind theprincipal point, and the view region is located Sm′=600 mm from theconcave mirror. Then, the virtual screen (VS) 5 having a diagonal lengthVSD of 181.9 mm, i.e., about 7.2 inches is floated in space and a VSP isabout 610 mm before the observer's eyes.

In this case, VSD/VSP is 0.298, ERD is 68.6 mm, a half angle OA extendedby the LCD relative to the projecting lens is 19.7 degrees and theeffective F number Fe is 1.7. Furthermore, the diameter of the viewregion ERD is 71.7 mm. Therefore, a slightly broader view region can beobtained as compared with the first preferred embodiment.

In fifth to eighth preferred embodiments, in the same manner as in thepreferred fourth preferred embodiment, a 1.35 type LCD (DLC=1.35 inch,about 34.3 mm) is used as a display element constituting the imagedisplay 1. Because of its high density and moderatecompactness/lightness, each of the fifth to eighth preferred embodimentsis used mainly as a display device of a mobile computer or a notebooktype personal computer, a display device of a portable video player orthe like or a display device installed in a vehicle (passenger's seat ina taxi) or the like. These preferred embodiments are the same as thefourth preferred embodiment in the optical system arrangement and thelike. Therefore, detailed numerical values of portions are shown in theTables 1 and 2 below, and further description is omitted.

In ninth to thirteenth preferred embodiments, a 3.3 type LCD (DLC=3.3inch, about 83.8 mm) is used as a display element constituting the imagedisplay 1. Each of the preferred embodiments is used as the displaydevice of a laptop (or usual notebook type) personal computer shown inFIG. 7 requiring a relatively large image plane, the desktop displaydevice for use in the desktop personal computer or another OA equipmentshown in FIG. 8, the display device for the personal TV which a patientcan watch in a hospital bed while lying therein as shown in FIG. 13, adisplay device of a personal TV on which a person can watch a favoriteprogram, video or the like without being interfered with by others or asanother display device for use in a broad application. These preferredembodiments are also the same as the fourth preferred embodiment in theoptical system arrangement and the like. Therefore, detailed numericalvalues of portions are shown in the Tables 1 and 2 below, and furtherdescription is omitted.

In fourteenth to nineteenth preferred embodiments, a 5-type CRT (DLC=5.0inches, i.e., 127 mm) with high definition is used as a display elementconstituting the image display 1 to obtain a bright and large imageplane having high definition. Each of the preferred embodiments is usedas a three-dimensional CAD VS display, the display for the capsuleoffice shown in FIG. 11, the display for the relaxation capsule shown inFIG. 12, the executive display shown in FIG. 14 or as another displaydevice for use in a broad application. An application as a high featuredversion of a personal TV or the like is also possible. These preferredembodiments are also the same as the fourth preferred embodiment in theoptical arrangement or the like. Therefore, detailed numerical values ofportions are shown in the Tables 1 and 2 below, and further descriptionis omitted.

TABLE 1 LIST 1 OF PREFERRED EMBODIMENTS VSD VSD DLC EMBODIMENT VSD/VSPVSP (mm) (inch) ERD (inch) 1 0.194 270.7 52.6 2.07 66.7 0.55 2 0.137444.3 60.7 2.39 71.7 0.55 3 0.109 469.7 51.3 2.02 88.9 0.55 4 0.298610.6 181.9 7.16 68.6 1.35 5 0.244 479.7 116.8 4.60 97.8 1.35 6 0.223488.4 109.0 4.29 96.0 1.35 7 0.278 491.8 136.9 5.39 48.9 1.35 8 0.306546.3 167.4 6.59 72.7 1.35 9 0.349 423.8 147.8 5.82 120.0 3.30 10 0.349610.0 212.9 8.38 120.0 3.30 11 0.454 685.3 310.9 12.24 94.3 3.30 120.476 771.9 367.5 14.47 78.6 3.30 13 0.524 888.9 465.6 18.33 83.3 3.3014 0.451 1025.9 462.5 18.21 125.7 5.00 15 0.484 1265.1 612.1 24.10 133.95.00 16 0.397 1280.0 508.0 20.00 166.7 5.00 17 0.423 1666.7 705.6 27.78170.5 5.00 18 0.353 3000.0 1058.4 41.67 204.5 5.00 19 0.106 2769.8 292.911.52 600.0 5.00

TABLE 2 LIST 2 OF PREFERRED EMBODIMENTS OA EMBODIMENT Fe (deg.) S1 PuD Ffl fm Sm Sm′ 1 1.1 11.0 −36.0 33.3 1.2 40.0 166.7 −250 500 2 1.4 12.3−32.0 22.2 1.8 40.0 190.5 −250 800 3 1.4 9.9 −40.0 27.8 1.8 50.0 190.5−250 800 4 1.7 19.7 −48.0 28.6 1.4 40.0 176.5 −250 600 5 1.4 21.3 −44.030.6 1.8 55.0 190.5 −250 800 6 1.6 19.7 −48.0 30.0 2.0 60.0 190.5 −250800 7 2.5 12.6 −77.0 30.6 1.8 55.0 153.8 −250 400 8 1.5 13.8 −70.0 45.51.1 50.0 153.8 −250 400 9 2.0 22.7 −100.0 50.0 2.0 100.0 176.5 −250 60010 2.0 29.2 −75.0 37.5 2.0 75.0 190.5 −250 800 11 2.0 28.6 −77.0 39.31.4 55.0 176.5 −250 600 12 2.2 25.5 −88.0 39.3 1.4 55.0 166.7 −250 50013 1.9 27.6 −80.0 41.7 1.2 50.0 166.7 −250 500 14 2.2 35.8 −88.0 39.31.4 55.0 190.5 −250 800 15 2.0 31.2 −105.0 53.6 1.4 75.0 285.7 −400 100016 1.9 38.4 −80.0 41.7 1.2 50.0 200.0 −250 1000 17 1.8 27.9 −120.0 68.21.1 75.0 285.7 −400 1000 18 1.8 27.9 −120.0 68.2 1.1 75.0 375.0 −5001500 19 2.0 32.4 −100.0 50.0 2.0 100.0 230.8 −250 3000

As described above, in the virtual screen (VS) display system accordingto preferred embodiments of the present invention, the image of theobject image displayed on a relatively small image display (micro CRT,LCD, DMD or the like) for displaying image information is projected andformed in a predetermined space and an observer observes the in-spacereal image via the field optical system in the specified position, and,by clarifying the physical range in which the principle of the VSdisplay system effectively works, a luminous, attractive, gentle toview, highly confidential and less energy consuming virtual screendisplay device is realized.

Moreover, the VS display device according to preferred embodiments ofthe present invention can be applied to a broad range of devices fromthe small-sized display device having superior portability for use in aportable TV, a portable TV phone, a portable video player, a mobilecomputer, a notebook computer or the like, and the middle-sized displaydevice of the desktop personal computer, a personal TV or the like to arelatively large-sized installation type display device such as acapsule office display, a relaxation capsule display, a executivedisplay and the like.

When the VS display device of preferred embodiments of the presentinvention is used as the display device of the computer or another OAequipment, the space on a desk occupied by the device is significantlyreduced as compared with the conventional CRT display. Furthermore,since the observer does not need to directly watch the CRT image planeor the like, eye fatigue is alleviated and health problems caused byelectromagnetic waves are avoided. Since the VS display device ofpreferred embodiments of the present invention is also provided with thefunction of adjusting the image forming position (optical axisdirection), a user can easily set the optimum image forming position(optical axis direction) at the time of use so that eye fatigue isfurther alleviated. Also, the device is convenient or favorableespecially for a presbyopic person because the virtual screen image canbe displayed in a visual distance that is within his or her reach.

Moreover, in the VS display device of preferred embodiments of thepresent invention, since the in-space image is displayed, the visualangle is narrowed according to the principle described above and therange in which the image plane is visible is restricted. Consideringthat the portable equipment, the personal computer, the personal TV orthe like is usually operated by an individual, a wide visual angle whichis difficult to be designed is unnecessary, and rather a narrow visualangle with high confidentiality (to allow the image displayed to beunviewable by others) is provided. Additionally, since the visual angleis narrow, the displayed image can be seen only by an operator withoutbothering others even if the display device is operated in the aircraft,the train, the common room in the hospital or another public place.

FIG. 15 shows a projector color image display device according toanother preferred embodiment of the present invention. In FIG. 15, aliquid crystal display panel 10 is arranged to function as a spacemodulation element. A plurality of light sources are provided includinga red light source (R light source) 12 for emitting a red light, a greenlight source (G light source) 14 for emitting a green light, and a bluelight source (B light source) 16 for emitting a blue light.

A dichroic prism 18 is arranged near the panel 10 to selectively reflector transmit the red light from the R light source 12, the green lightfrom the G light source 14 and the blue light from the B light source 16so as to synthesize the red, green and blue lights to irradiate thespace modulation element 10. The dichroic prism 18 preferably includes asubstantially rectangular parallelepiped configuration (shown in asquare configuration in FIG. 15) in which dichroic filter films 181 and183 cross substantially perpendicularly to each other.

A light source drive includes a power switching circuit 22 and drivecircuits 201, 203 and 205. The light source drive circuits 201, 203 and205 are electrically connected to a respective one of the R light source12, the G light source 14 and the B light source 16 to turn on and offthe R light source 12, the G light source 14 and the B light source 16,respectively. The light source drive circuits 201, 203 and 205preferably have power sources built therein, so that light-emittingpower currents of the light sources can be adjusted manually or via anexternal controller.

An image processing circuit 24 and a three-color separation imageprocessing circuit 26 are also provided and operate as described below.The image processing circuit 24 and the three-color separation imageprocessing circuit 26 constitute an image information input.

An image forming lens 32 is provided for projecting light fluxestransmitted from the liquid crystal display 10 to form an image.

The R light source 12, the G light source 14 and the B light source 16preferably include LEDs which are adapted to radiate red, green and redlights, respectively. The R light source 12, the G light source 14 andthe B light source 16 and the liquid crystal panel 10 are arranged tosurround the four sides of the substantially rectangular dichroic prism18. On a surface of the liquid crystal panel 10 on the side of thedichroic prism 18, a micro lens array 30 is preferably disposed tocontact the liquid crystal panel 10.

The dichroic filter film 181 in the dichroic prism 18 reflects the redlight and transmits the green and blue lights. The dichroic filter film183 reflects the blue light and transmits the red and green lights.Therefore, when the R light source 12 is lit, the radiated red light isreflected by the dichroic filter film 181 in the dichroic prism 18,transmitted through the dichroic filter film 183 and radiated via themicro lens array 30 to the liquid crystal panel 10. When the G lightsource 14 is lit, the radiated green light is transmitted through thedichroic filter films 181 and 183 and radiated via the micro lens array30 to the liquid crystal panel 10. When the B light source 16 is lit,the radiated blue light is reflected by the dichroic filter film 183,transmitted through the dichroic filter film 181 and radiated via themicro lens array 30 to the liquid crystal panel 10.

The power source switching circuit 22 receives a command from a controlcircuit 28 to switch the power sources of the light source drivecircuits 201, 203 and 205. Through this switching, the R light source12, the G light source 14 and the B light source 16 are turned on andoff.

An image to be displayed is entered as an image signal to the imageprocessing circuit 24. The image processing circuit 24 is controlled bythe control circuit 28 to image-process the input image signal in a modewhich can be displayed on the liquid crystal panel 10, and transmits aprocessing result to the three-color separation image processing circuit26. The three-color separation image processing circuit 26image-processes and separates the entered image information into a redcomponent image, a green component image and a blue component image,successively switches the red, green and blue component images at a highspeed and displays the red, green and blue component images on the spacemodulation element 10.

The control circuit 28 constituting the controller of the apparatuscontrols the image information input 24 and 26 in such a manner that thered, green and blue component images of the color image to be displayed(entered as the image signal) are successively switched at a high speedand displayed on the space modulation element 10, and controls the lightsource drive unit 201, 203, 205 and 22 to successively switch on and offthe R, G and B light sources exclusively at a high speed andperiodically repeat the lighting in such a manner that only the R lightsource 12 is lit when the red component image is displayed on the spacemodulation element 10, only the G light source 14 is lit when the greencomponent image is displayed and only the B light source 16 is lit whenthe blue component image is displayed.

Therefore, the red, green and blue component images displayed on theliquid crystal panel 10 are irradiated with the red, green and bluelights, respectively. At this time, each color light is effectivelycollected at an opening of each picture element by the micro lens array30 (in which individual micro lenses are arranged to have a one-to-onecorrespondence with individual picture elements of the liquid crystalpanel), and efficiency of light use is greatly improved.

In this manner, the red, green and blue component images aresuccessively switched and displayed in the red, green and blue lights onthe liquid crystal panel 10 as an object plane of the image forming lens32. When these images are projected via the image forming lens 32 toform an image on a screen or another display medium, the red componentimage via the red light, the green component image via the green lightand the blue component image via the blue light are successivelyswitched to form the image on the display medium. When the speed of theswitching becomes sufficiently high, these three color images aresynthesized and visually recognized as the color image in human eyes.

In the above description, the high speed at which the red, green andblue component images are successively switched and displayed on thespace modulation element and the R, G and B light sources aresuccessively turned on and off exclusively to periodically repeat thelighting indicates a speed at which the component images are switched onthe display medium in such a manner that the color image is visuallyrecognized by the human eyes.

Specifically, the preferred embodiment shown in FIG. 15 preferablyincludes: a space modulation element 10 having a two-dimensionalarrangement of picture elements having a light transmittance that can becontrolled and arranged to display an image to be displayed as atwo-dimensional transmittance distribution; the R light source 12 whichemits the red light; the G light source 14 which emits the green light;the B light source 16 which emits the blue light; the dichroic prism 18for selectively reflecting or transmitting the red light from the Rlight source 12, the green light from the G light source 14 and the bluelight from the B light source 16 to irradiate the space modulationelement 10; the image forming lens 32 for projecting the light fluxestransmitted through the space modulation element 10 to form the image;the image information input 24 and 26 for inputting the imageinformation of the image to be displayed to the space modulation element10; the light source drive 201, 203, 205 and 22 for turning on and offthe R, G and B light sources 12, 14 and 16; and the controller 28 whichcontrols the image information input 24 and 26 in such a manner that thered, green and blue component images of the color image to be displayedare successively switched at a high speed and displayed on the spacemodulation element 10 and controls the light source drive 201, 203, 205and 22 to successively switch on and off the R, G and B light sourcesexclusively at a high speed and periodically repeat the lighting in sucha manner that only the R light source 12 is lit when the red componentimage is displayed on the space modulation element 10, only the G lightsource 14 is lit when the green component image is displayed and onlythe B light source 16 is lit when the blue component image is displayed.The R, G and B light sources 12, 14 and 16 preferably include LEDs whichradiate red, green and blue lights, respectively.

The dichroic prism 18 is preferably a substantially rectangularparallelepiped prism which has the dichroic filter film 181 forreflecting the light and transmitting the green and blue lights and thedichroic filter film 183 for transmitting the red light reflected by thedichroic filter film 181 and the green light and reflecting the bluelight. The R, G and B light sources 12, 14 and 16 and the spacemodulation element 10 are arranged to surround the four surfaces of thedichroic prism 18 as seen in FIG. 15. The space modulation elementpreferably comprises a liquid crystal panel 10. The micro lens array 30for enhancing the incident efficiency of the irradiation light to eachpicture element is provided on the incident side of the irradiationlight of the liquid crystal panel 10 which functions as the spacemodulation element.

Additionally, in the control mode of the control circuit 28, bydisplaying a single-color image on the liquid crystal panel 10 andlighting the R, G and B light sources 12, 14 and 16 simultaneously,successively or selectively, a monochromatic image may be displayed. Inthis case, by lighting one or two of the light sources, themonochromatic image can be displayed in various colors. Alternatively,for example, by alternately switching and displaying the red and bluecomponent images and synchronously turning on/off the R and B lightsources, the two component images can be synthesized and displayed as ayellow image.

FIG. 16 is an explanatory view showing an arrangement of the liquidcrystal panel, the light sources, the dichroic prism and the imageforming lens of the preferred embodiment shown in FIG. 15.

A projector base 200 is provided in the apparatus shown in FIG. 16. Apanel connector 101 is provided on the base 200 and supports the panel10 thereon. Also provided on the base 200 are an R light sourceconnector 123, a G light source connector 143, a B light sourceconnector 163, a prism support 181 and a lens support 320.

Panel electrodes 10A are disposed on the liquid crystal panel 10 as seenin FIG. 16. When the liquid crystal panel 10 is plugged into the panelconnector 101, lead electrodes formed on the panel connector 101 areelectrically connected to the panel electrodes 10A. The micro lens array30 is preferably connected to the liquid crystal panel 10.

The G light source 14, which is shown as representation of the otherlight sources 16, 18, preferably includes a plurality of LEDs adapted toemit green lights (abbreviated as G-LED) 140 and arranged on a lightsource panel 141 which is preferably formed of an aluminum plate or thelike in such a manner that the G-LEDs can be turned on and off. A lightsource panel electrode is disposed on a portion of the light sourcepanel 141 to be plugged into the G light source connector 143 (on whicha lead electrode is formed). As shown in FIG. 16, when the light sourcepanel 141 is engaged with the G light source connector 143, the panelelectrode is connected to the lead electrode. A cooling fin 142 ispreferably provided to function as the cooling device on a rear surfaceof the light source panel 141. The R and B light sources not shown inFIG. 16 have an arrangement and are adapted to be mounted to theprojector base 200 similar to those of the G light source 14.

By adjusting the number of G-LEDs arranged on the light source panel141, the light emitting quantity of the light source can be adjusted.Furthermore, by adjusting the light emitting electric current to the LEDin each light source panel, the light emitting quantity of each lightsource is adjusted, so that a desired color balance can be achieved.Moreover, by cooling the LED with the cooling fin, the light emittingluminance of the LED can be effectively improved.

The dichroic prism 18 is preferably engaged and fixed on the prismsupport 181, and the image forming lens 32 is positioned on the lenssupport 320. The lens support 320 is provided with a reference groove, areference pin or another positioning means (not shown). The imageforming lens 32 is located by the positioning means.

In this manner, after each member is assembled onto the projector base200, each section is covered with a lid for entirely covering theprojector base 200 or with the lid and a side surface cover in such amanner that each section is positioned in a target position.Additionally, the image information input, the light source drive, thecontroller and the power source or another electric system may bedisposed inside the projector body constituted as aforementioned ordisposed separately from the body.

In the preferred embodiment shown in FIG. 16, the R, G and B lightsources preferably include the cooling devices 142. Also, the spacemodulation element 10, the R, G and B light sources 12, 14 and 16, thedichroic prism 18 and the image forming lens 32 are arranged on the samebase 200.

FIG. 18 is a view showing the basic concept of a virtual screen (VS)display device related to another preferred embodiment of the presentinvention. In an example, the display device is provided with a display1 for displaying image information, a projection element 2 forprojecting and forming an image of the display 1 as an object image in apredetermined space and an optical focusing element 3 for directing alight flux from a projected in-space image toward an observer's eyes.

The display 1 preferably comprises a CRT (cathode ray tube), an LCD(liquid crystal display), a DMD (digital mirror device) or anotherdisplay which can display an output from a computer, a TV (television)image plane or the like. When the display 1 is CRT, an additional lightsource is unnecessary. In the case of LCD, however, a lighting source, adiffusion plate, a filter and the like are necessary on the rear surfaceof the display 1 as shown in FIG. 18.

The optical focusing element 3 for directing the light flux for formingan image in a position of a real screen (RS) 4 (the image formingposition when there is no optical focusing system) toward the observer'seyes changes the direction of the light flux with a positive power,forms an in-space image in a position of a virtual screen (VS) 5 (theimage of the real screen RS as an object of the optical focusing system)and brings a divergent light flux from the in-space image to a viewregion 6 in a range in which the observer's eyes are to be placed. Asthe optical focusing element 3, a positive lens or another transmissiontype image forming element is shown in FIG. 18, but a concave mirror oranother reflective image forming element, a Fresnel optical element, ora hologram or another optical diffraction element can be used as theoptical focusing element 3.

In preferred embodiments of the present invention, the virtual screenshown in FIG. 18 is formed for each of right and left eyes in such amanner that a stereoscopic image can be seen. The stereoscopic displaydevice is preferably provided with two displays and two projectionelements for both eyes and one optical focusing element for bringinglight fluxes from two in-space images projected by the two projectionelements to two predetermined view regions, respectively. Examples ofpreferred embodiments of the present invention will be described.

FIG. 17 is a view showing one preferred embodiment of the presentinvention. In FIG. 17, a left-eye display 1-1, a right-eye display 1-2,a left-eye projection element 2-1, a right-eye projection element 2-2,an optical focusing element 3, a left-eye virtual screen (VS) 5-1, aright-eye virtual screen (VS) 5-2, a left-eye view region 6-1 and aright-eye view region 6-2 are provided in the preferred embodiment showntherein.

In FIG. 17, a light flux emanating from the left-eye display 1-1 isoperated by the left-eye projection element 2-1 in such a manner that animage is formed at a position of a real screen (RS) (not shown), anddirected toward the optical focusing element 3. The optical focusingelement 3 has a positive power to direct the incident light flux towardthe left-eye view region 6-1 and additionally contribute to the imageforming. Then, an image is formed on the left-eye VS 5-1. After theimage forming, the light flux is diverged and passed through theleft-eye view region 6-1. The optical focusing element 3 functions insuch a manner that the light flux having each image height forms animage in the vicinity of the left-eye VS 5-1 and is directed to theleft-eye view region 6-1. Thereby, when a left-eye pupil is placed inthe left-eye view region 6-1, all the images having heights of theimages of the left-eye display 1-1 can be seen at the same time.

In the same manner as for the left eye, the processing for the right eyeis performed from the right-eye display 1-2 to the right-eye view region6-2. Therefore, when a right eye pupil is placed in the right-eye viewregion 6-2, images having heights of all the images of the right-eyedisplay 1-2 can be seen at the same time.

It is preferred that an interval between centers of the two view regions6-1 and 6-2 is substantially equal to about 60 mm to about 70 mm andthat the two view regions 6-1 and 6-2 abut against each other in atransverse direction or overlap each other slightly (by about 7 mm orless). In the system, although the left-eye VS 5-1 and the right-eye VS5-2 overlap each other with a large area (for the convenience ofillustration, in FIG. 1, the two VSs are deviated toward the opticalaxis of the optical focusing system, but actually they are deviated onlyslightly), information from the displays 1-1, 1-2 are brought toward theright and left eyes without interference. Furthermore, a range in whicha stereoscopic image is visible is relatively broad, e.g., about 60 mmto about 70 mm.

FIG. 19 is a view showing another preferred embodiment of the invention.In FIG. 19, the apparatus includes a left-eye display 1-1, a left-eyeprojection element 2-1, an optical focusing system 3, a left-eye virtualscreen (VS) 5-1, a left-eye view region 6-1, a right-eye view region6-2, and a left-eye bent mirror 7-1.

In FIG. 19, a light flux emanating from the left-eye display 1-1 isoperated by the left-eye projection element 2-1 in such a manner that animage is formed in a position of a real screen (RS) (not shown), anddirected toward the optical focusing system 3. In this case, the opticalfocusing system 3 is a concave mirror as shown, a hologram elementfunctioning in a similar manner, a Fresnel element or the like, and hasa positive power to direct the incident light flux toward the left-eyeview region 6-1 and additionally contribute to the image forming. Then,an image is formed on the left-eye VS 5-1. After the image forming, thelight flux is diverged and passed through the left-eye view region 6-1.The optical focusing element 3 functions in such a manner that the lightflux having each image height forms an image in the vicinity of theleft-eye VS 5-1 and is directed to the left-eye view region 6-1.Thereby, when a left-eye pupil is placed in the left-eye view region6-1, all the images having heights of the images of the left-eye display1-1 can be seen at the same time.

Here, the bent mirror 7-1 is used to facilitate the arrangement.Therefore, the optical axis of the optical focusing element 3 is notnecessarily disposed perpendicular to the optical axis of the projectionelement 2-1 as shown in FIG. 19, and can be disposed substantially inparallel therewith. Furthermore, if necessary, the bent mirror 7-1 maybe a half mirror. If possible, the arrangement without the bent mirrorcan be used.

To prevent FIG. 19 from being complicated, only the right-eye viewregion 6-2 is shown for the right eye and other parts of the device isomitted, but the arrangement for the right eye is symmetrical with thatfor the left-eye. In the same manner as for the left eye, the processingfor the right eye is performed from the right-eye display to theright-eye view region 6-2. Therefore, when a right eye pupil is placedin the right-eye view region 6-2, images having heights of all theimages of the right-eye display can be seen at the same time.

Here, characteristic respects are, in the same manner as in thepreferred embodiment shown in FIG. 17, that an interval between centersof the two view regions 6-1 and 6-2 is approximately equal to about 60mm to about 70 mm and that the two view regions 6-1 and 6-2 abut againsteach other in a transverse direction or overlap each other slightly byabout 7 mm or less. In the system, although the left-eye VS 5-1 and theright-eye VS (not shown) overlap each other at a large area, informationfrom the displays are brought toward the right and left eyes withoutinterference. Furthermore, a range in which a stereoscopic image isvisible is relatively broad, e.g., about 60 mm to about 70 mm.

FIG. 20 shows still another preferred embodiment of the presentinvention, and shows an example of a display device similar to a virtualscreen display device of the applicant's prior application (JapanesePatent Application No. 9-57947/1997). In the prior-application displaydevice, a plane image is displayed on a virtual screen, but in thepreferred embodiment shown in FIG. 20, a stereoscopic image can be seenin substantially the same mode as in the prior application. In thepreferred embodiment of FIG. 20, as in the preferred embodiments ofFIGS. 17 and 19, optical systems other than a combiner (the opticalfocusing element 3 in FIGS. 17 and 19) are necessary both for right andleft eyes. In FIG. 20, however, the optical system elements for botheyes are overlapped because the example is seen from a side view, andonly one-side view is shown.

In FIG. 20, there are projectors 10 each provided with a display elementand an optical projection system for right and left eyes. A light fluxfrom each projector 10 is reflected by the bent mirror 20, thenreflected and converged by a combiner 30, and enlarged to form an imagein a position of a virtual screen (VS) 41 or 42. As a result, it seemsto the operator's eyes 50 as if there is an enlarged display element inthe VS position. At this time, the synthesis system of the opticalsystem of the projector 10 and the combiner 30 is operated in such amanner that the VS 41 or 42 and the display element of the projector 10form a conjugate relationship. On the other hand, the synthesis systemof the optical lighting system and the optical projection system of theprojector 10 and the combiner 30 is operated in such a manner that theoperator's eyes 50 are in a conjugate positional relationship with thelight source in the projector.

The combiner of the preferred embodiment shown in FIG. 20 preferablyincludes an optical diffraction element 31 which forms a hologramdiffraction grating on a transparent base plate. Therefore, light fluxescan be collected in a direction which does not follow a reflection lawon a flat surface as shown in FIG. 20. A similar operation can beperformed by a concave mirror or a Fresnel mirror, but in this case, ahalf mirror or an appropriate reflectance or transmittance is necessary.

Furthermore, in FIG. 20, a see-through coefficient adjustment plate 32is preferably provided and includes a PF-LCD (plastic/flexible liquidcrystal). By electrically adjusting the transmittance, the see-throughcoefficient of the combiner 30 can be regulated.

The position of the virtual screen (VS) can be set optionally in theposition 41 or 42 shown in FIG. 20 in accordance with the capability ofthe operator's eyes or the type of the operation. For example, the VSposition 41 is an example in which the VS is set at the same visualdegree as for a presbyopic person. The VS position 42 indicates a casein which a person talks while simultaneously seeing the other person anddata indicated by the projected image during a meeting or the like.Further, the VS can be set in an indefinite distance.

As described above, in the virtual screen stereoscopic display device ofpreferred embodiments of the present invention, since the light fluxesfrom the image displays for right and left eyes are brought to both eyeswithout interference, the stereoscopic image can be easily seen withoutrequiring special glasses or the like. Furthermore, the virtual screenis not a so-called virtual image but a real image which is formed inspace. Substantially all of the light fluxes related with the imageforming are brought to the eyes. Therefore, a very bright stereoscopicimage with a luminance equal to the luminance of the image display isachieved. The device can thus contribute to the saving of power orenergy. When the virtual screen stereoscopic display device is used as acomputer terminal, an occupying space on a desk is remarkably reduced ascompared with a conventional CRT display. Furthermore, a CRT image planedoes not need to be seen directly. Therefore, eye fatigue is alleviatedand health problems caused by electromagnetic waves are avoided.

Moreover, by providing the adjustment function of the image formingposition (optical axis direction) as shown in the preferred embodimentof FIG. 20, the image forming position (optical axis direction) which isoptimum for a user can be easily set at the time of operation, which canalleviate eye fatigue. Further, since the display can be positioned at avisual distance within a reach of a viewer, the device is convenient andfavorable especially for a presbyopic person. Furthermore, by providingthe combiner (optical focusing system) with the see-through function asshown in the preferred embodiment of FIG. 20, people can talk with eachother while seeing the stereoscopically displayed data without lookingdown. Therefore, the device is capable of being used on a desk duringthe meeting or a lecture (for a lecturer, students and the like) andalso can be used for a TV conference. Additionally, the device can alsobe used as a tele-prompter (a device with which a manuscript can be readwithout looking down) for the lecturer or an announcer. When thestereoscopic display is unnecessary, the same information can bepresented on the right and left sides. Alternatively, by presentingdifferent information not related with the stereoscopic display, thedifferent information can be seen in each view region.

Furthermore, by providing the function of changing the see-throughcoefficient of the combiner (optical focusing system) as shown in thepreferred embodiment of FIG. 20, the favorite see-through condition canbe set in accordance with the environment. For example, the foregroundis made unseen during work, but when talking with a person in front orat the time of the meeting, the see-through coefficient can be raised.Thereby, a working environment which previously easily caused stress, isnow easily controlled by an operator/viewer to avoid any visual ormental stress or fatigue.

In the virtual screen stereoscopic display device, since the in-spaceimage is seen, a visual angle is narrowed in principle, and a range inwhich an image plane is visible is restricted. However, considering thecomputer terminal is used usually by each individual person, a broadvisual angle difficult to be designed is unnecessary, and rather anarrow visual angle with a high confidentiality is welcomed.

While preferred embodiments of the invention have been disclosed,various modes of carrying out the principles disclosed herein arecontemplated as being within the scope of the following claims.Therefore, it is understood that the scope of the invention is not to belimited except as otherwise set forth in the claims.

What is claimed is:
 1. A virtual screen stereoscopic display apparatus,comprising: at least two displays arranged to display characters andimage information; at least two optical projection elements arranged toenlarge, project and form real images of object images displayed by theat least two displays in a display space, the real images formed by theat least two optical projection elements being projected in-spaceimages; and at least one optical focusing system arranged to positionlight fluxes received from the two projected in-space images at twopredetermined view regions, respectively; wherein centers of said twoview regions are spaced apart from each other in a transverse direction,wherein said at least two displays have an effective diagonal lengthDLC; said at least two optical projection elements have an effective Fnumber which is defined by Fe=S1/PuD wherein S1 is a distance betweenthe display and a principal point of the two optical projection elementsand PuD is a diameter of an exit pupil of the two optical projectionelements; and wherein a diameter of a range in which the image isviewable to the observer in the view region is ERD and a diagonal lengthof the virtual screen is VSD and a distance between the virtual screenand the view region is VSP, and the following equation is satisfied:VSD/VSP=DLC/(ERD×Fe).
 2. The virtual screen stereoscopic displayapparatus according to claim 1, wherein the centers of said two viewregions are spaced from each other by an approximate distance of about60 mm to 70 mm.
 3. The virtual screen stereoscopic display apparatusaccording to claim 1, wherein said two view regions are overlapped byabout 7 mm or less.
 4. The virtual screen stereoscopic display apparatusaccording to claim 1, wherein each of said two displays comprises atleast one of a cathode ray tube, a liquid crystal display, a digitalmirror device and a display means which can display an output from acomputer, a television or display generating device.
 5. The virtualscreen stereoscopic display apparatus according to claim 1, wherein saidtwo displays are arranged to display right-eye image information on aleft side and left-eye image information on a right side when a personis opposed to the two displays.
 6. The virtual screen stereoscopicdisplay apparatus according to claim 1, wherein said optical focusingsystem comprises at least one of a concave mirror, a reflective imageforming element, a positive lens, a transmission type image formingelement, a Fresnel optical element, a hologram and an opticaldiffraction element.
 7. A virtual screen stereoscopic display apparatus,comprising: at least two display means for displaying characters andimage information; at least two optical projection means for enlarging,projecting and forming real images of object images displayed by the atleast two displays in a display space, the real images formed by the atleast two optical projection means being projected in-space images; andat least one optical focusing means for positioning light fluxesreceived from the two projected in-space images at two predeterminedview regions, respectively; wherein centers of said two view regions arespaced apart from each other in a transverse direction, wherein said atleast two display means have an effective diagonal length DLC; said atleast two optical projection means have an effective F number which isdefined by Fe=S1/PuD wherein S1 is a distance between the display and aprincipal point of the two optical projection means and PuD is adiameter of an exit pupil of the two optical projection means; andwherein a diameter of a range in which the image is viewable to theobserver in the view region is ERD and a diagonal length of the virtualscreen is VSD and a distance between the virtual screen and the viewregion is VSP, and the following equation is satisfied:VSD/VSP=DLC/(ERD×Fe).
 8. The virtual screen stereoscopic displayapparatus according to claim 7, wherein the centers of said two viewregions are spaced from each other by an approximate distance of about60 mm to 70 mm.
 9. The virtual screen stereoscopic display apparatusaccording to claim 7, wherein said two view regions are overlapped byabout 7 mm or less.
 10. The virtual screen stereoscopic displayapparatus according to claim 7, wherein each of said two display meanscomprises at least one of a cathode ray tube, a liquid crystal display,a digital mirror device and a display means which can display an outputfrom a computer, a television or display generating device.
 11. Thevirtual screen stereoscopic display apparatus according to claim 7,wherein said two display means are arranged to display right-eye imageinformation on a left side and left-eye image information on a rightside when a person is opposed to the two display means.
 12. The virtualscreen stereoscopic display apparatus according to claim 7, wherein saidoptical focusing means comprises at least one of a concave mirror, areflective image forming element, a positive lens, a transmission typeimage forming element, a Fresnel optical element, a hologram and anoptical diffraction element.